1. Field of the Invention
The present invention generally relates to a semiconductor device having columnar electrodes, and to a method for manufacturing a semiconductor device having pin wires.
2. Description of the Related Art
Hitherto, there have been known semiconductor packages each having a resin-sealed semiconductor chip. Semiconductor packages are becoming increasingly smaller. Recently, a semiconductor package having nearly the same size as a semiconductor chip has emerged. Such a semiconductor package is called, for example, a CSP (Chip Size Package).
One method for manufacturing CSPs consists of the steps of forming integrated circuits and electrode pads on a wafer, and then forming columnar electrodes connected to the electrode pads on the wafer, and subsequently sealing the surface of the wafer and the columnar electrodes with resin, and upon completion of the sealing, dicing the wafer to thereby separate semiconductor packages, which include semiconductor chips, from the wafer (see, for instance, Japanese Unexamined Patent Publication (Kokai) No. 9-64049).
A resin layer is formed in such a way as to have nearly the same height as the columnar electrode. A tip end of the columnar electrode is exposed from the surface of the resin layer. An external terminal (or electrode pad) to be connected to each of the columnar electrodes is formed on the resin layer. A solder bump can be provided on this external terminal. Further, a rewiring conductor portion constituted by a conductor pattern is formed on the surface of the wafer, so that the positions of the columnar electrodes differ from those of the electrode pads formed on the wafer.
Moreover, Japanese Unexamined Patent Publication (Kokai) No. 9-260428 discloses that a semiconductor chip is mounted on a mounting substrate by using a metallic wire. An end of the metallic wire is bonded to the electrode pad of the semiconductor chip, while the other end thereof is connected to the mounting substrate by solder. With this constitution, stress generated due to the difference in amount of thermal expansion between the semiconductor chip and the mounting substrate can be absorbed by warpage of the metallic wire.
In the case of using the semiconductor device mounted on the circuit substrate, the external terminal (or solder bump) of the semiconductor device is connected to the electrode pad of the circuit substrate. The semiconductor chip of the semiconductor device faces the circuit substrate thereof across the sealing resin thereof. When the semiconductor device is used, thermal stress is generated in the external terminals and the columnar electrodes owing to the difference in amount of thermal expansion between the semiconductor chip and the substrate of the semiconductor device. Thus, the external terminals and the columnar electrodes become fatigued by repetitive generation of thermal stress.
This thermal stress is directly proportional to the difference in amount of thermal expansion between the semiconductor chip and the circuit substrate of the semiconductor device, and is inversely proportional to the thickness of the sealing resin layer. It is, therefore, preferable for alleviating the stress to increase the thickness of the sealing resin layer. It is, however, necessary, for increasing the thickness of the sealing resin layer, to lengthen the columnar electrodes. Usually, the columnar electrodes are formed by plating. However, there is a limit to a possible increase in the length of the columnar electrodes formed by plating.
Thus, when the columnar electrodes are formed from a (bonding) wire, the columnar electrodes can be lengthened, so that the sealing resin layer can be thickened. However, in the case of using a wire processed by a wire bonder as the columnar electrode, such a wire is too thin to be used as the columnar electrode. Hence, it is desired to make a columnar electrode formed from a wire of sufficient length and strength.
Furthermore, a wire, from which a sufficiently long columnar electrode can be provided, has flexibility. Thus, even when thermal stress is applied on the columnar electrode that is constituted by the wire, the columnar electrode is not destroyed. However, when the sealing resin layer of the semiconductor electrode is hard, large stress is exerted on a joint portion between the columnar electrode, which is constituted by the wire restrained by the sealing resin, and the external terminal fixed to the circuit substrate. It is, therefore, preferable that the sealing resin of the semiconductor device should be as soft as possible.
Further, such a conventional semiconductor device has a drawback in that pressure is applied onto the entire wafer and the wafer is thus damaged when an end portion of the columnar electrode is adjusted by being grounded, and that the flow of resin sometimes causes undesired deformation of the columnar electrode when sealed with the resin.
On the other hand, in recent years, semiconductor devices are required not only to be light and small, but also to operate at a high speed and have an advanced function. In the case that a semiconductor chip is mounted on a device, such as an interposer and a mother board, there has been developed a method of mounting a flip chip device as the semiconductor device, which meets the aforementioned demands, by using solder balls. This conventional method, however, has the following drawbacks. That is, because of a narrow pitch between the electrode pads of the semiconductor chip, the solder balls to be used for connection are specifically designed in such a manner as to have small ball diameters and to show less variation in characteristics thereof and are thus very expensive. Further, because an underfill to be used for sealing the circuit surface is required to have a property by which no voids are generated when filling the narrow gap between the semiconductor chip and the mother board, it is often true that the underfill is specifically designed so as to improve the flowability and adhesionability thereof according to each of the specifications of the semiconductor chip and the mother board. Consequently, the cost of the flip-chip semiconductor device is high.
Additionally, there have been developed a connection method using an adhesive, which contains conductive particles, and another connection method using stud bumps. When using these conventional methods, variation in adhesion is caused owing to the warpage of the semiconductor chip, voids and the leveling accuracy of the terminal thereof. Thus, these conventional methods are low in reliability. There is a fear that the cost of managing such variations will increase.
In the case of the method of mounting the flip chip device, it is possible that metallic wires can be used instead of using solder balls. The use of metallic wires is expedited in the conventional wire bonding system by using an automatic wire bonder. However, in the conventional wire boding system, a tip end of the metallic wire is joined to an end portion of the semiconductor chip. Then, a desired portion of the metallic wire is connected to the electrode of the mother board. Subsequently, a capillary is moved to thereby pull and cut the metallic wire. In this case, the metallic wire is torn off. Thus, the conventional system has a drawback in that the section of the metallic wire is not of a uniform shape, and that the length of the torn metallic wire is not uniform.
An object of the present invention is to provide a semiconductor device that has superior durability to thermal stress.
To solve such problems, according to an aspect of the present invention, there is provided a semiconductor device which comprises a semiconductor element having a plurality of electrode pads, a plurality of columnar electrodes connected to the plurality of electrode pads, a resin layer covering the semiconductor element and said columnar electrodes and having a surface, and outer terminals disposed on the surface of the resin layer in such a way as to be electrically connected to the columnar electrodes. Each of the columnar electrodes includes a wire portion extending from the electrode pad of the semiconductor element, and an enlarged portion extending from the outer terminals and having a cross-sectional area greater than that of the wire portion thereof.
In this constitution, wires can be used as the columnar electrodes. Thus, the columnar electrodes can be formed in such a manner as to simultaneously have sufficient length, flexibility, and strength. Consequently, the length of the columnar electrodes and the thickness of the sealing resin layer can be increased. Hence, a semiconductor device having superior durability to thermal fatigue can be obtained.
Preferably, the resin layer comprises a first soft resin sub-layer formed on a surface of the semiconductor element and a second resin sub-layer disposed on the opposite side of the first resin sub-layer from the semiconductor element and having elasticity higher than that of the first resin sub-layer.
Preferably, the columnar electrode comprises an extension part of the wire portion subjected to a wall thickening treatment. Alternatively, the enlarged portion of the columnar electrode includes an electrically conductive material attached to the wire portion thereof.
Moreover, according to another aspect of the present invention, there is provided a semiconductor device which comprises a semiconductor element having a plurality of electrode pads, a plurality of columnar electrodes connected to the electrode pads, a resin layer covering the semiconductor element and said columnar electrodes and having a surface, outer terminals disposed on the surface of the resin layer in such a way as to be electrically connected to the columnar electrodes, and re-wiring conductor portions provided between the electrode pads and the columnar electrodes of the semiconductor element. The resin layer is made of relatively soft spin-coated resin.
In this constitution, the resin layer is made of relatively soft spin-coated resin. This imparts flexibility to the portion between the columnar electrodes and the external terminals formed in the semiconductor chip. Thus, the reliability of the joint portion between the columnar electrodes and the outer terminals against thermal stress and mechanical stress can be ensured. Especially, the combination of the soft resin and the soft columnar electrode imparts high flexibility to the sealing resin layer and the columnar electrodes against thermal fatigue. Consequently, a semiconductor device having superior durability to thermal fatigue can be obtained.
Preferably, the resin layer is made of one of a silicon resin and an epoxy resin. These resins are suitable for spin coating.
The columnar electrode comprises a wire. Further, each of the columnar electrodes is formed by partially expanding a wire. Alternatively, the columnar electrode is formed by joining a plurality of wires into a single columnar electrode.
Preferably, the semiconductor device further comprises dummy electrodes disposed in the resin layer substantially parallel to the columnar electrodes. Alternatively, the semiconductor device further comprises a resin column disposed in the resin layer in such a manner as to be nearly parallel to the columnar electrodes.
Furthermore, according to another aspect of the present invention, there is provided a semiconductor device which comprises a semiconductor element having a plurality of electrode pads, a plurality of columnar electrodes connected to the electrode pads, a resin layer covering the semiconductor element and the columnar electrodes and having a surface, re-wiring conductor portions provided on the surface of the resin layer in such a way as to be connected to the columnar electrodes, an insulating layer covering the resin layer and a part of the re-wiring conductor portion, and outer terminals electrically connected to part of the re-wiring conductor portions, which part is exposed from the insulating layer.
In this constitution, the re-wiring conductor portions are provided on the surface of the resin layer. Moreover, the insulating layer covers the resin layer and a part of the re-wiring conductor portions. The outer terminals are electrically connected to the part of the re-wiring conductor portions, which is exposed from the insulating layer. The re-wiring conductor portion is not covered with the resin layer. Thus, the re-wiring conductor portion has flexibility.
Furthermore, according to another aspect of the present invention, there is provided a method for manufacturing a semiconductor device, which comprises the steps of half-cutting metallic wires at desired positions, which have a first ends, bonding the first ends of the metallic wires to electrode portions of a semiconductor element or a semiconductor device, and cutting each of the metallic wires at the desired positions by pulling the metallic wires relative to the electrode portions, to thereby form pin wires. The pin wires have a cut second ends.
In this constitution, half-cutting is performed on the metallic wires at the desired positions. Then, after the first ends of the metallic wires are bonded to the electrode portions of the semiconductor element, each of the metallic wires is reliably and completely cut at the desired positions when the metallic wires is pulled to the electrode portions. The wire portions of the metallic wires have a uniform shape. The metallic wires have uniform length. Therefore, in the case of the semiconductor element having a plurality of pin wires, the pitch of which is narrow, the plurality of pin wires have nearly constant height. Thus, the semiconductor element is rendered suitable for being joined to other devices, such as a mother board.